Conversion of Amorphous MOF Microspheres into a Nickel Phosphate Battery-Type Electrode Using the "Anticollapse" Two-Step Strategy.

Abstract

Metal-organic frameworks (MOFs) have attracted great attention as templates for preparation of functional porous materials owing to their adjustable structures, rich porosity, and controllable components. However, collapsed templates during the conversion process hinder their application and synthesis of derivatives. In this study, we demonstrate a novel two-step etching strategy during which amorphous MOF microspheres are initially transformed into nickel hydroxide and then subsequently transformed into microspherical nickel phosphates. Through this strategy, the prepared nickel phosphates maintain the microspherical morphology of MOFs but with no MOF residuals, exhibiting ultrahigh specific surface area, uniform pore size, and good structural robustness. Examined as a supercapacitor electrode, they show an outstanding specific capacity of 820 C g-1 at 0.5 A g-1 and remarkable cycling stability of 88% capacity retention after 10 000 cycles. Moreover, an asymmetric supercapacitor constructed utilizing reduced graphene cross-linked with p-phenylenediamine oxide (PPD-rGO) as the cathode displays a preeminent energy density of 64.56 Wh kg-1 at a power density of 507 W kg-1. This strategy has important significance in guiding the preparation of high-performance MOF-derived electrodes.